5274
J. Am. Chem. Soc. 1998, 120, 5274-5278
Responsive Supramolecular Polythiophene Assemblies Karim Faı1d and Mario Leclerc* Contribution from the De´ partement de Chimie, UniVersite´ de Montre´ al, Montre´ al, Que´ bec, Canada H3C 3J7 ReceiVed January 26, 1998
Abstract: The simple preparation of a novel family of smart polymers based on acid-base complexes between an acidic conjugated polymer (poly(2-(4-methyl-3-thienyloxy)ethanesulfonic acid)) and various amine-containing molecules is described. The neutralization of the acid form of the polymer can be monitored optically in real time through the decrease of the 800 nm absorption band, characteristic of a self-acid-doped state. Moreover, by electrostatically binding adequate responsive substituents, thermochromic, ionochromic, photochromic, and biochromic materials have been easily developed. These optical features seem related to a conformational change of the conjugated main chain driven by side-chain disordering. Furthermore, aminosilane-treated substrates can undergo further modification through electrostatic interactions with partially pre-neutralized polymers, yielding very efficient electrochemical solid-state sensors. It is believed that such a simple methodology, based on electroactive and photoactive supramolecular polymeric assemblies, may open the way to the design of integrated chemical systems incorporating both a trigger and a transducer and can find applications in the areas of biosensors, drug screening, and diagnostics.
Introduction The search for smart polymers is an exploding research field due to the high demand for materials capable of carrying out increasingly complex tasks and performing various functions. In this respect, functionalized regioregular π-conjugated polythiophenes are a very promising class of materials exhibiting impressive chromic responses upon exposure to specific stimuli,1 opening the way to the design of a variety of sensory devices. For instance, these polymers, bearing adequately designed side chains, can undergo striking conformational changes when exposed to heat, light, or various chemical and biochemical moieties giving rise to thermochromism, photochromism, ionochromism, or even biochromism. These optical transitions, from deep violet (maximum of absorption around 550 nm) to bright yellow (maximum of absorption near 400 nm), are believed to be related to a planar-to-nonplanar (from highly conjugated to less conjugated) conformational transition of the backbone. Indeed, in conjugated polymers, there is a strong correlation between the electronic structure and the backbone conformation, any change in the main chain conformation leading to a modification of the effective conjugation length associated with a shift of the absorption in the UV-visible range. However, studies on different polythiophene derivatives have suggested that this conformational modification of the main chain could be driven by order-disorder transitions of the side chains, sidechain disordering disrupting planar polythiophene assemblies.1 A similar approach was also developed with functionalized π-conjugated polydiacetylenes2,3 and σ-conjugated polysilanes.4 However, in all cases, the detection or recognition event is * To whom correspondence should be addressed. Present address: Centre de Recherche en Science et Inge´nierie des Macromole´cules, De´partement de Chimie, Universite´ Laval, Que´bec, PQ, Canada G1K 7P4. (1) Leclerc, M.; Faı¨d, K. AdV. Mater. 1997, 9, 1087. (2) Charych, D. H.; Nagy, J. O.; Spevak, W.; Bednarski, M. D. Science 1993, 261, 585. (3) Cheng, Q.; Stevens, R. C. AdV. Mater. 1997, 9, 481. (4) Yuan, C. H.; West, R. D. J. Chem. Soc., Chem. Commun. 1997, 1825.
mainly a function of the nature and characteristics of the side chains, requiring the cumbersome design, synthesis, and purification of numerous monomeric and polymeric derivatives. In this paper, we report a novel and simple method to introduce the required side chains through the use of acid-base interactions. Indeed, it is shown here that poly(2-(4-methyl-3thienyloxy)ethanesulfonic acid)5 can react with various basic molecules to yield tunable, functionalized (through electrostatic interactions), and chromic polymers. New responsive, both in solution and in the solid state, polymers can then be easily prepared and utilized to detect a large number of different and targeted external stimuli. Moreover, the electroactivity of these polymers also allows the development of versatile and tunable electrochemical devices. Results and Discussion As recently reported,5 self-acid-doped (presumably, an acidcatalyzed oxidation by oxygen of the polythiophene) poly(2(4-methyl-3-thienyloxy)ethanesulfonic acid) (PMTOES) exhibits a large absorption band around 800 nm, characteristic of an oxidized and conducting (5 S/cm) form. Stepwise addition of sodium hydroxide aliquots resulted in a progressive neutralization of the polymer, with the neutral and insulating (
